Multiple location load control system

ABSTRACT

A multiple location load control system comprises a main device and remote devices, which do not require neutral connections, but allow for visual and audible feedback at the main device and the remote devices. The main device and the remote devices are adapted to be coupled together via an accessory wiring. The main device can be wired on the line side and the load side of the load control system. The main device is configured to enable a charging path to allow the remote devices to charge power supplies through the accessory wiring during a first time period of a half cycle of the AC power source. The main device and the remote devices are configured to communicate with each other via the accessory wiring during a second time period of the half cycle, for example, by actively pulling-up and actively pulling-down the accessory wiring to communicate using tri-state logic.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.62/245,763, filed Oct. 23, 2015, which is incorporated by referenceherein as if fully set forth.

BACKGROUND

Three-way and four-way switch systems for use in controlling electricalloads, such as lighting loads, are known in the art. Typically, theswitches are coupled together in series electrical connection between analternating-current (AC) power source and the lighting load. Theswitches are subjected to an AC source voltage and carry full loadcurrent between the AC power source and the lighting load, as opposed tolow-voltage switch systems that operate at low voltage and low current,and communicate digital commands (usually low-voltage logic levels) to aremote controller that controls the level of AC power delivered to theload in response to the commands. Thus, as used herein, the terms“three-way switch”, “three-way system”, “four-way switch”, and “four-waysystem” mean such switches and systems that are subjected to the ACsource voltage and carry the full load current.

A three-way switch derives its name from the fact that it has threeterminals and is more commonly known as a single-pole double-throw(SPDT) switch, but will be referred to herein as a “three-way switch”.Note that in some countries a three-way switch as described above isknown as a “two-way switch”.

A four-way switch is a double-pole double-throw (DPDT) switch that iswired internally for polarity-reversal applications. A four-way switchis commonly called an intermediate switch, but will be referred toherein as a “four-way switch”.

In a typical, prior art three-way switch system, two three-way switchescontrol a single lighting load, and each switch is fully operable toindependently control the load, irrespective of the status of the otherswitch. In such a three-way switch system, one three-way switch must bewired at the AC power source side of the system (sometimes called “lineside”), and the other three-way switch must be wired at the lightingload side of the system.

FIG. 1A shows a standard three-way switch system 100, which includes twothree-way switches 102, 104. The switches 102, 104 are connected betweenan AC power source 106 and a lighting load 108. The three-way switches102, 104 each include “movable” (or common) contacts, which areelectrically connected to the AC power source 106 and the lighting load108, respectively. The three-way switches 102, 104 also each include twofixed contacts. When the movable contacts are making contact with theupper fixed contacts, the three-way switches 102, 104 are in position Ain FIG. 1A. When the movable contacts are making contact with the lowerfixed contact, the three-way switches 102, 104 are in position B. Whenthe three-way switches 102, 104 are both in position A (or both inposition B), the circuit of system 100 is complete and the lighting load108 is energized. When switch 102 is in position A and switch 104 is inposition B (or vice versa), the circuit is not complete and the lightingload 108 is not energized.

Three-way dimmer switches that replace three-way switches are known inthe art. An example of a three-way dimmer switch system 150, includingone prior art three-way dimmer switch 152 and one three-way switch 104is shown in FIG. 1B. The three-way dimmer switch 152 includes a dimmercircuit 152A and a three-way switch 152B. A typical, AC phase controldimmer circuit 152A regulates the amount of energy supplied to thelighting load 108 by conducting for some portion of each half cycle ofthe AC waveform, and not conducting for the remainder of the half cycle.Because the dimmer circuit 152A is in series with the lighting load 108,the longer the dimmer circuit conducts, the more energy will bedelivered to the lighting load 108. Where the lighting load 108 is alamp, the more energy that is delivered to the lighting load 108, thegreater the light intensity level of the lamp. In a typical dimmingoperation, a user may adjust a control to set the light intensity levelof the lamp to a desired light intensity level. The portion of each halfcycle for which the dimmer conducts is based on the selected lightintensity level. The user is able to dim and toggle the lighting load108 from the three-way dimmer switch 152 and is only able to toggle thelighting load from the three-way switch 104. Since two dimmer circuitscannot be wired in series, the three-way dimmer switch system 150 canonly include one three-way dimmer switch 152, which can be located oneither the line side or the load side of the system.

A four-way switch system is required when there are more than two switchlocations from which to control the load. For example, a four-way systemrequires two three-way switches and one four-way switch, wired in wellknown fashion, so as to render each switch fully operable toindependently control the load irrespective of the status of any otherswitches in the system. In the four-way system, the four-way switch isrequired to be wired between the two three-way switches in order for allswitches to operate independently, i.e., one three-way switch must bewired at the AC source side of the system, the other three-way switchmust be wired at the load side of the system, and the four-way switchmust be electrically situated between the two three-way switches.

FIG. 1C shows a prior art four-way switching system 180. The system 180includes two three-way switches 102, 104 and a four-way switch 185. Thefour-way switch 185 has two states. In the first state, node A1 isconnected to node A2 and node B1 is connected to node B2. When thefour-way switch 185 is toggled, the switch changes to the second statein which the paths are now crossed (i.e., node A1 is connected to nodeB2 and node B1 is connected to node A2). Note that a four-way switch canfunction as a three-way switch if one terminal is simply not connected.

FIG. 1D shows another prior art switching system 190 containing aplurality of four-way switches 185. As shown, any number of four-wayswitches can be included between the three-way switches 102, 104 toenable multiple location control of the lighting load 108.

Multiple location dimming systems employing a smart dimmer and one ormore specially-designed remote (or “accessory”) dimmers have beendeveloped. The remote dimmers permit the intensity level of the lightingload to be adjusted from multiple locations. A smart dimmer is one thatincludes a microcontroller or other processing means for providing anadvanced set of control features and feedback options to the end user.For example, the advanced features of a smart dimmer may include aprotected or locked lighting preset, fading, and double-tap to fullintensity. The microcontroller controls the operation of thesemiconductor switch to thus control the intensity of the lighting load.

To power the microcontroller, the smart dimmers include power supplies,which draw a small amount of current through the lighting load when thesemiconductor switch is non-conductive each half cycle. The power supplytypically uses this small amount of current to charge a storagecapacitor and develop a direct-current (DC) voltage to power themicrocontroller. An example of a multiple location lighting controlsystem, including a wall-mountable smart dimmer switch andwall-mountable remote switches for wiring at all locations of a multiplelocation dimming system, is disclosed in commonly assigned U.S. Pat. No.5,248,919, issued on Sep. 28, 1993, entitled LIGHTING CONTROL DEVICE,which is herein incorporated by reference in its entirety.

Referring again to the system 150 of FIG. 1B, since no load currentflows through the dimmer circuit 152A of the three-way dimmer switch 152when the circuit between the AC power source 106 and the lighting load108 is broken by either three-way switch 152B or 104, the dimmer switch152 is not able to include a power supply and a microcontroller. Thus,the dimmer switch 152 is not able to provide the advanced set offeatures of a smart dimmer to the end user.

FIG. 2 shows an example multiple location lighting control system 200including one wall-mountable smart dimmer 202 and one wall-mountableremote dimmer 204. The dimmer 202 has a hot (H) terminal for receipt ofan AC source voltage provided by an AC power source 206, and adimmed-hot (DH) terminal for providing a dimmed-hot (or phasecontrolled) voltage to a lighting load 208. The remote dimmer 204 isconnected in series with the DH terminal of the dimmer 202 and thelighting load 208, and passes the dimmed-hot voltage through to thelighting load 208.

The dimmer 202 and the remote dimmer 204 both have actuators to allowfor raising, lowering, and toggling on/off the light intensity level ofthe lighting load 208. The dimmer 202 is responsive to actuation of anyof these actuators to alter the intensity level or to power the lightingload 208 on/off accordingly. In particular, an actuation of an actuatorat the remote dimmer 204 causes an AC control signal, or partiallyrectified AC control signal, to be communicated from that remote dimmer204 to the dimmer 202 over the wiring between the accessory dimmer (AD)terminal (i.e., accessory terminal) of the remote dimmer 204 and the ADterminal of the dimmer 202. The dimmer 202 is responsive to receipt ofthe control signal to alter the dimming level or toggle the load 208on/off. Thus, the load can be fully controlled from the remote dimmer204.

The user interface of the dimmer 202 of the multiple location lightingcontrol system 200 is shown in FIG. 3. As shown, the dimmer 202 mayinclude a faceplate 310, a bezel 312, an intensity selection actuator314 for selecting a desired level of light intensity of a lighting load208 controlled by the dimmer 202, and a control switch actuator 316. Anactuation of the upper portion 314A of the actuator 314 increases orraises the light intensity of the lighting load 208, while an actuationof the lower portion 314B of the actuator 314 decreases or lowers thelight intensity.

The dimmer 202 may also include a visual display in the form of aplurality of light sources 318, such as light-emitting diodes (LEDs).The light sources 318 may be arranged in an array (such as a lineararray as shown), and are illuminated to represent a range of lightintensity levels of the lighting load 208 being controlled. Theintensity levels of the lighting load 208 may range from a minimumintensity level, which may be the lowest visible intensity, but whichmay be “full off”, or 0%, to a maximum intensity level, which istypically “full on”, or substantially 100%. Light intensity level istypically expressed as a percent of full intensity. Thus, when thelighting load 208 is on, light intensity level may range from 1% tosubstantially 100%.

FIG. 4 is a simplified block diagram of the dimmer 202 and the remotedimmer 204 of the multiple location lighting control system 200. Thedimmer 202 includes a bidirectional semiconductor switch 420, e.g., atriac or two field-effect transistors (FETs) in anti-series connection,coupled between the hot terminal H and the dimmed-hot terminal DH, tocontrol the current through, and thus the light intensity of, thelighting load 208. The semiconductor switch 420 has a control input (orgate), which is connected to a gate drive circuit 424. The input to thegate renders the semiconductor switch 420 conductive or non-conductive,which in turn controls the power supplied to the lighting load 208. Thegate drive circuit 424 provides control inputs to the semiconductorswitch 420 in response to command signals from a microcontroller 426.

The microcontroller 426 receives inputs from a zero-crossing detector430 and a signal detector 432 and controls the semiconductor switch 420accordingly. The microcontroller 426 also generates command signals to aplurality of LEDs 418 for providing feedback to the user of the dimmer202. A power supply 428 generates a DC output voltage V_(CC) to powerthe microcontroller 426. The power supply is coupled between the hotterminal H and the dimmed hot terminal DH.

The zero-crossing detector 430 determines the zero-crossings of theinput AC supply voltage from the AC power supply 206. A zero-crossing isdefined as the time at which the AC supply voltage transitions frompositive to negative polarity (i.e., a negative-going zero-crossing), orfrom negative to positive polarity (i.e., a positive-goingzero-crossing), at the beginning of each half cycle. The zero-crossinginformation is provided as an input to microcontroller 426. Themicrocontroller 426 provides the gate control signals to operate thesemiconductor switch 420 to provide voltage from the AC power source 206to the lighting load 208 at predetermined times relative to thezero-crossing points of the AC waveform.

Generally, two techniques are used for controlling the power supplied tothe lighting load 208: forward phase control dimming and reverse phasecontrol dimming. In forward phase control dimming, the semiconductorswitch 420 is turned on at some point (e.g., a firing angle or atransition time) within each AC line voltage half cycle and remains onuntil the next voltage zero-crossing. Forward phase control dimming isoften used to control energy to a resistive or inductive load, which mayinclude, for example, a magnetic low-voltage transformer or anincandescent lamp. In reverse phase control dimming, the semiconductorswitch 420 is turned on at the zero-crossing of the AC line voltage andturned off at some point (e.g., a firing angle or a transition time)within each half cycle of the AC line voltage. Reverse phase control isoften used to control energy to a capacitive load, which may include,for example, an electronic low-voltage transformer. Since thesemiconductor switch 420 must be conductive at the beginning of the halfcycle, and be able to be turned off with in the half cycle, reversephase control dimming requires that the dimmer have two FETs inanti-serial connection, or the like.

The signal detector 432 has an input 440 for receiving switch closuresignals from momentary switches T, R, and L. Switch T corresponds to atoggle switch controlled by the switch actuator 316, and switches R andL correspond to the raise and lower switches controlled by the upperportion 314A and the lower portion 314B, respectively, of the intensityselection actuator 314.

Closure of switch T connects the input of the signal detector 432 to theDH terminal of the dimmer 202, and allows both positive and negativehalf cycles of the AC current to flow through the signal detector.Closure of switches R and L also connects the input of the signaldetector 432 to the DH terminal. However, when switch R is closed,current only flows through the signal detector 432 during the positivehalf cycles of the AC power source 406 because of a diode 434. Insimilar manner, when switch L is closed, current only flows through thesignal detector 432 during the negative half cycles because of a diode436. The signal detector 432 detects when the switches T, R, and L areclosed, and provides two separate output signals representative of thestate of the switches as inputs to the microcontroller 426. A signal onthe first output of the signal detector 432 indicates a closure ofswitch R and a signal on the second output indicates a closure of switchL. Simultaneous signals on both outputs represents a closure of switchT. The microprocessor controller 426 determines the duration of closurein response to inputs from the signal detector 432.

The remote dimmer 204 provides a means for controlling the dimmer 202from a remote location in a separate wall box. The remote dimmer 204includes a further set of momentary switches T′, R′, and L′ and diodes434′ and 436′. The wire connection is made between the AD terminal ofthe remote dimmer 204 and the AD terminal of the dimmer 202 to allow forthe communication of actuator presses at the remote switch. The ADterminal is connected to the input 440 of the signal detector 432. Theaction of switches T′, R′, and L′ in the remote dimmer 204 correspondsto the action of switches T, R, and L in the dimmer 202.

Since the remote dimmer 204 does not have LEDs, no feedback can beprovided to a user at the remote dimmer 204. Therefore there is a needfor multiple location dimming system in which the remote devices includevisual displays for providing feedback to a user.

SUMMARY

The present disclosure relates to multiple location load control systemshaving multiple smart load control devices, and more particularly, amultiple location dimming system that includes a smart dimmer and one ormore remote dimmers for controlling the amount of power delivered to alighting load, where all of the smart dimmers and the remote dimmers areoperable to display a present intensity level of the lighting load on avisual indicator.

A load control device may be responsive to a remote control device in aload control system for controlling an amount of power delivered from anAC power source to an electrical load. The remote control device may beadapted to be coupled to the load control device via an electrical wire.The load control device may comprise a controllably conductive deviceadapted to be electrically coupled in series between the AC power sourceand the electrical load, a control circuit configured to control thecontrollably conductive device to control the amount of power deliveredto the electrical load (e.g., using a forward phase control technique ora reverse phase control technique), and a communication circuit adaptedto be coupled to the electrical wire. The control circuit may beconfigured to render the controllably conductive device conductive(e.g., when using the forward phase control technique) or non-conductive(e.g., when using the reverse phase control technique) at a transitiontime during a half cycle of the AC power source. The communicationcircuit may be configured to conduct a charging current for a powersupply of the remote control device through the electrical wire. Thecommunication circuit may be responsive to the control circuit tocontrol the electrical wire between an active pull-up state and anactive pull-down state to transmit a digital message to the remotecontrol device via the electrical wire. The control circuit may beconfigured to control the communication circuit to generate a highimpedance state on the electrical wire when the communication circuit isnot transmitting a digital message to the remote control device. Thecontrol circuit may be further configured to control the communicationcircuit to provide the active pull-up state (e.g., when using theforward phase control technique) or the active pull-down state (e.g.,when using the reverse phase control technique) on the electrical wireduring a period of time around the transition time of the controllablyconductive device when the communication circuit is not transmitting adigital message to the remote control device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a diagram of an example of a prior art three-way switchsystem, which includes two three-way switches.

FIG. 1B is a diagram of an example of a prior art three-way dimmerswitch system including one prior art three-way dimmer switch and onethree-way switch.

FIG. 1C is a diagram of an example of a prior art four-way switchingsystem.

FIG. 1D is a diagram of an example of a prior art extended four-wayswitching system.

FIG. 2 is a diagram of an example of a prior art multiple locationlighting control system having a dimmer switch and a remote switch.

FIG. 3 is a front view of an example of a user interface of the dimmerswitch of the multiple location lighting control system of FIG. 2.

FIG. 4 is a diagram of an example of the dimmer switch and the remoteswitch of the multiple location lighting control system of FIG. 2.

FIG. 5A is a block diagram of an example of a multiple location loadcontrol system.

FIG. 5B is a block diagram of an example of a multiple location loadcontrol system.

FIG. 6 is a perspective view of an example of a user interface of a loadcontrol device.

FIG. 7 is a block diagram of an example main load control device of amultiple location system.

FIG. 8A is a block diagram of an example remote load control device of amultiple location system.

FIG. 8B is a block diagram of another example remote load control deviceof a multiple location system.

FIG. 9 is an example schematic diagram of the multi-location circuit andcontrol circuit of the main load control device and the multi-locationcircuit and control circuit of the remote load control device of thesystem of FIG. 5A or FIG. 5B.

FIG. 10A is a timing diagram of an example of a complete line cycle ofan AC voltage waveform provided by an AC power source.

FIG. 10B is a timing diagram of example waveforms illustrating theoperation of a main dimmer of a multiple location load control systemwhen using a reverse phase control dimming technique.

FIG. 11 is a diagram of an example of a payload format for communicationbetween the main load control device and the remote load control deviceof the system of FIG. 5A or FIG. 5B.

FIG. 12 is a flowchart of an example of a user interface procedureexecuted by the control circuit of the main load control device of FIG.7.

FIG. 13 is a flowchart of an example of an Idle routine of the userinterface procedure of FIG. 12.

FIG. 14 is a flowchart of an example of an ActiveHold routine of theuser interface procedure of FIG. 12.

FIG. 15 is a flowchart of an example of a Release routine of the userinterface procedure of FIG. 12.

FIG. 16 is a flowchart of an example of a RX buffer procedure executedby the control circuit of the main load control device of FIG. 7.

FIG. 17 is a flowchart of an example of a multi-location controlprocedure executed by the control circuit of the main load controldevice of FIG. 7.

FIG. 18 is a flowchart of an example of a multi-location controlprocedure executed by the control circuit of the remote load controldevice of FIG. 8A or FIG. 8B.

FIG. 19 is a flowchart of an example of a load control procedureexecuted by the control circuit of the main load control device of FIG.7.

DETAILED DESCRIPTION

FIG. 5A is a block diagram of an example of a multiple location loadcontrol system, e.g., a multiple location dimming system 500. Themultiple location dimming system 500 may comprise a main load controldevice, e.g., a main dimmer 502, and one or more remote load controldevices, e.g., two remote dimmers 504 (i.e., accessory dimmers). Themain dimmer 502 and remote dimmers 504 may be coupled in serieselectrical connection between an AC power source 506 and a lighting load508, for example, via a traveler wiring 511. The traveler wiring 511 maycouple the AC power source 506 to the lighting load 508 via the maindimmer 502 and one or more remote dimmers 504, for example, to providepower to the lighting load 508. Neutral wiring 512 may couple thelighting load 508 back to the AC power source 506, for example, toprovide a return path for any remaining power provided by the AC powersource 506 and not dissipated by the lighting load 508.

The main dimmer 502 may be wired to the line side of the system 500(e.g., as shown) or the load side of the system 500. Although thedescription herein is primarily with reference to the main dimmer 502wired to the line side of the system 500, one or more embodiments maycomprise the main dimmer 502 wired to the load side of the system 500(e.g., and one or more remote dimmers 504 wired to the line side,accordingly). Further, any number of (e.g., more than two) remotedimmers 504 may be provided in the multiple location dimming system 500.

The main dimmer 502 may comprise a first main terminal and a second mainterminal. For example, the main dimmer 502 may comprise a hot terminal H(i.e., a line-side load terminal) adapted to be coupled to the line-sideof the system 500 and a dimmed-hot terminal DH (i.e., a load-sideterminal) adapted to be coupled to the load-side of the system 500. Themain dimmer 502 may comprise a load control circuit coupled between thehot and dimmed-hot terminals for controlling the amount of powerdelivered to the lighting load 508 (e.g., as described with reference toFIG. 7). The remote dimmers 504 may comprise a first main terminal and asecond main terminal. For example, the remote dimmers 504 may comprisetwo hot terminals H1, H2, which may conduct the load current from the ACpower source 506 to the lighting load 508. The main dimmer 502 and theremote dimmers 504 may each comprise an internal air-gap switch (e.g.,air-gap switches 722, 822 shown in FIGS. 7 and 8A) for disconnecting thelighting load 508 from the AC power source 506. The main dimmer 502 andthe remote dimmers 504 may each comprise an accessory dimmer (AD)terminal AD (i.e., accessory terminal) coupled together via a singleaccessory dimmer (AD) line 509 (i.e., an accessory wiring). The maindimmer 502 and the remote dimmers 504 may be operable to communicate,i.e., transmit and receive digital messages, via the AD line 509. Themain dimmer 502 and the remote dimmers 504 may not include connectionsto the neutral side of the AC power source 506.

The main dimmer 502 and the remote dimmer 504 may include actuators andvisual displays, such that lighting load 508 may be controlled from andfeedback of the lighting load may be provided at each of the main dimmer502 and the remote dimmers 504. In order to provide the visual displaysat the remote dimmers 504, the remote dimmers 504 may include a controlcircuit (e.g., which may comprise a microprocessor) and a power supplyfor powering the microprocessor. The main dimmer 502 may provide an ADsupply voltage VAD (e.g., approximately 80-170 VDC) on the AD line 509to enable the power supplies of the remote dimmers 504 to charge duringa first portion (i.e., a charging time T_(CHRG)) of a half cycle of theAC power source 506. During a second portion (i.e., a communication timeT_(COMM)) of the half cycle, the main dimmer 502 and the remote dimmers504 are operable to transmit and receive the digital messages via the ADline 509.

FIG. 5B is a block diagram of an example of a multiple location loadcontrol system, e.g., a multiple location dimming system 510. Themultiple location dimming system 510 may comprise a main load controldevice, e.g., a main dimmer 502, and one or more remote load controldevices, e.g., two remote dimmers 514 (i.e., accessory dimmers). Theremote dimmers 514 may be substantially similar to the remote dimmers504, except the remote dimmers 514 may comprise a single main terminal(e.g., a single hot terminal H′) as opposed to the first and second hotterminals H1 and H2 and may not comprise an air-gap switch (e.g., theair-gap switch 822 shown in FIG. 8A). One or more of the embodimentsdescribed herein with reference to the multiple location dimming system500 and/or the remote dimmers 504 may be applicable to the multiplelocation dimming system 510 and/or the remote dimmers 514.

The main dimmer 502 may be coupled in series electrical connectionbetween the AC power source 506 and the lighting load 508, for example,via traveler wiring 511. The traveler wiring 511 may couple the AC powersource 506 to the lighting load 508 via the main dimmer 502, forexample, to provide power to the lighting load 508. The one or moreremote dimmers 514 may be coupled to the traveler wiring 511 via the hotterminal H′. Neutral wiring 512 may couple the lighting load 508 back tothe AC power source 506, for example, to provide a return path for anyremaining power provided by the AC power source 506 and not dissipatedby the lighting load 508. The main dimmer 502 may be wired to the lineside of the system 510 (e.g., as shown) or the load side of the system510. Although the description herein is primarily with reference to themain dimmer 502 wired to the line side of the system 510, one or moreembodiments may comprise the main dimmer 502 wired to the load side ofthe system 510 (e.g., and one or more remote dimmers 514 wired to theline side, accordingly). Further, any number of (e.g., more than two)remote dimmers 514 may be provided in the multiple location dimmingsystem 510.

The hot terminal H′ of the remote dimmers 514 may be connected to thedimmed hot terminal DH of the main dimmer 502 (e.g., as shown) and tothe lighting load 508 via the traveler wiring 511, for example, if themain dimmer 502 is wired to the line side of the system 510. If the maindimer 502 is wired to the load side of the system 510, then the hotterminal H′ of the remote dimmers 514 may be connected to the hotterminal H of the main dimmer 502 and to the AC power source 506 via thetraveler wiring 511. The main dimmer 502 and the remote dimmers 514 mayeach comprise accessory dimmer terminals AD (i.e., accessory terminals)coupled together via a single accessory dimmer (AD) line 509 (i.e., anaccessory wiring). The main dimmer 502 and the remote dimmers 514 may beoperable to communicate, i.e., transmit and receive digital messages,via the AD line 509. The main dimmer 502 and the remote dimmers 514 mayor may not include connections to the neutral side of the AC powersource 506.

The main dimmer 502 and the remote dimmer 514 may include actuators andvisual displays, such that lighting load 508 may be controlled from andfeedback of the lighting load may be provided at each of the main dimmer502 and the remote dimmers 514. In order to provide the visual displaysat the remote dimmers 514, the remote dimmers 514 may include a controlcircuit (e.g., which may comprise a microprocessor) and a power supplyfor powering the microprocessor. The main dimmer 502 may provide an ADsupply voltage VAD (e.g., approximately 80-170 VDC) on the AD line 509to enable the power supplies of the remote dimmers 514 to charge duringa first portion (i.e., a charging time T_(CHRG)) of a half cycle of theAC power source 506. During a second portion (i.e., a communication timeT_(COMM)) of the half cycle, the main dimmer 502 and the remote dimmers514 are operable to transmit and receive the digital messages via the ADline 509.

FIG. 6 is a diagram of an example user interface 600 of a load controldevice, which may be provided on, for example, the main dimmer 502and/or the remote dimmers 504, 514 of the multiple location dimmingsystem 500 shown in FIG. 5A and/or the multiple location dimming system510 shown in FIG. 5B. The user interface 600 may include a thin touchsensitive actuator 610 comprising an actuation member 612 having firstand second portions 612A, 612B. The actuation member 612 may extendthrough a bezel 614 to contact a touch sensitive device (not shown)located inside the main dimmer 502 and the remote dimmers 504, 514. Themain dimmer 502 may be operable to control the intensity of a connectedlighting load 508 in response to actuations of the actuation member 612of either the main dimmer 502 or the remote dimmers 504, 514.

The user interface 600 may comprise a faceplate 616, which may include anon-standard opening 618 and may mount to an adapter 620. The bezel 614may be housed behind the faceplate 616 and extend through the opening618. The adapter 620 may connect to a yoke (not shown), which may beadapted to mount the main dimmer 502 and the remote dimmers 504, 514 tostandard electrical wallboxes. An air-gap actuator 622 may allow foractuation of an internal air-gap switch (e.g., an internal air-gapswitch 722 as shown in FIG. 7) by pulling the air-gap actuator 622 down.

The bezel 614 may comprise a break 624, which may separate the lowerportion 612A and the upper portion 612B of the actuation member 612.Upon actuation of the lower portion 612B of the actuation member 612,the main dimmer 502 may cause the connected lighting load 508 to togglefrom on to off, and vice versa. Actuation of the upper portion 612A ofthe actuation member 612, i.e., above the break 624, may cause theintensity of the lighting load 508 to change to a level dependent uponthe position of the actuation along the length of the actuation member612.

A plurality of visual indicators, e.g., a plurality of light-emittingdiodes (LEDs), may be arranged in a linear array behind the actuationmember 612. The actuation member 612 may be substantially transparent,such that the LEDs are operable to illuminate portions of the actuationmember. Two different color LEDs may be located behind the lower portion612B, such that the lower portion is illuminated, for example, withwhite light when the lighting load 508 is on and with orange light withthe lighting load is off. The LEDs behind the upper portion 612A may be,for example, white and may be illuminated as a bar graph to display theintensity of the lighting load 508 when the lighting load is on.

The touch sensitive actuator 610 of the user interface 600 may bedescribed in greater detail in commonly-assigned U.S. Pat. No.7,791,595, issued Sep. 7, 2010, entitled TOUCH SCREEN ASSEMBLY FOR ALIGHTING CONTROL, the entire disclosure of which is hereby incorporatedby reference.

FIG. 7 is a block diagram of an example main load control device of amultiple location load control system, e.g., the main dimmer 502. Themain dimmer 502 may comprise a controllably conductive device 710, agate drive circuit 712, a control circuit 714, a zero-crossing detectcircuit 716, a memory 718, an audible sound generator 720, an air-gapswitch 722, a communication circuit 725, the user interface 600, and/ora multi-location circuit 732.

The controllably conductive device 710 may comprise a bidirectionalsemiconductor switch coupled between the hot terminal H and the dimmedhot terminal DH, to control the current through, and thus the intensityof, the lighting load 508. The controllably conductive device 710 may beimplemented as any suitable bidirectional semiconductor switch, such as,for example, a thyristor (such as a triac or one or more siliconcontrolled rectifiers), a FET in a full-wave rectifier bridge, two FETsin anti-series connection, or one or more insulated-gate bipolarjunction transistors (IGBTs). The controllably conductive device 710 maycomprise a control input (e.g., gate), which is connected to the gatedrive circuit 712. The input to the gate may render the controllablyconductive device 710 selectively conductive or non-conductive, which inturn may control the power supplied to the lighting load 508.

The control circuit 714 may be operable to control the controllablyconductive device 710 by providing a control signal to the gate drivecircuit 712 using the forward phase control dimming technique and/or thereverse phase control dimming technique. For example, the controlcircuit 714 may comprise a microcontroller, a microprocessor, aprogrammable logic device (PLD), a field programmable grid array (FPGA),an application specific integrated circuit (ASIC), or any suitableprocessing device, controller, or control circuit. The control circuit714 may be coupled to a zero-crossing detect circuit 716, which maydetermine the zero-crossing points of the AC line voltage from the ACpower supply 506. As shown in FIG. 7, the zero-crossing detect circuit716 may be coupled between the hot terminal H and the dimmed hotterminal DH. In addition, the zero-crossing detect circuit 716 may becoupled between the hot terminal H and a neutral terminal (e.g., thatmay be coupled to the neutral wiring 512). The control circuit 714 maygenerate the gate control signals to operate the controllably conductivedevice 710 to thus provide voltage from the AC power supply 506 to thelighting load 508 at predetermined times relative to the zero-crossingpoints of the AC line voltage.

The user interface 600 may be coupled to the control circuit 714, suchthat the control circuit 714 is operable to receive inputs from thetouch sensitive actuator 610 and to control the LEDs to provide feedbackof the amount of power presently being delivered to the lighting load508. An example of the electrical circuitry of the user interface 600may be described in greater detail in co-pending, commonly-assigned U.S.Pat. No. 7,855,543, issued Dec. 21, 2010, entitled FORCE INVARIANT TOUCHSENSITIVE ACTUATOR, the entire disclosure of which is herebyincorporated by reference.

The main dimmer 502 may further comprise an audible sound generator 718coupled to the control circuit 714. The control circuit 714 may beoperable to cause the audible sound generator 718 to produce an audiblesound in response to an actuation of the touch sensitive actuator 610. Amemory 718 may be coupled to the control circuit 714 and may be operableto store control information of the main dimmer 502.

The air-gap switch 722 may be coupled in series between the hot terminalH and the controllably conductive device 710. The air-gap switch 722 mayhave a normally-closed state in which the controllably conductive device710 is coupled in series electrical connection between the AC powersource 506 and the lighting load 508. When the air-gap switch 722 isactuated (i.e., in an open state), the air-gap switch may provide anactual air-gap break between the AC power source 506 and the lightingload 508. The air-gap switch 722 may allow a user to service thelighting load 508 without the risk of electrical shock.

The main dimmer 502 may comprise a power supply 730 for generating a DCsupply voltage V_(CC) (e.g., approximately 3.3 volts) for powering thecontrol circuit 714 and other low voltage circuitry of the main dimmer502. The power supply 730 may draw (e.g., only draw) current at thebeginning of a half cycle (e.g., each half cycle) while the controllablyconductive device 710 is non-conductive, for example, if the forwardphase control dimming technique is used. The power supply 730 may draw(e.g., only draw) current at the end (i.e., trailing edge) of a halfcycle (e.g., each half cycle) while the controllably conductive device710 is non-conductive, for example, if the reverse phase control dimmingtechnique is used. The power supply 730 may stop drawing current whenthe controllably conductive device 710 is rendered conductive.

The multi-location circuit 732 may be coupled between the hot terminal Hand/or the dimmed hot terminal DH and an accessory dimmer terminal AD(which may be adapted to be coupled to the AD line 509). Themulti-location circuit 732 may provide a supply voltage to the remotedimmer 504, 514 via the AD line 509 and/or allow for communication of adigital message between the main dimmer 502 and the remote dimmers 504,514 via the AD line 509. The control circuit 714 may provide a controlsignal to the multi-location circuit. If the main dimmer 502 is locatedon the line side of the system 500/510, then the control circuit 714 maycontrol the multi-location circuit 732 to allow the remote dimmers 504,514 to charge their internal power supplies and transmit and receivedigital messages during the positive half cycles. If the main dimmer 502is located on the load side of the system 500/510, then the controlcircuit 714 may control the multi-location circuit 732 to allow theremote dimmers 504, 514 to charge their internal power supplies andtransmit and receive digital messages during the negative half cycles.

The main dimmer 502 may comprise another communication circuit 725(e.g., in addition to the multi-location circuit 732) for transmittingor receiving digital messages via a communications link, for example, awired serial control link, a power-line carrier (PLC) communicationlink, or a wireless communication link, such as an infrared (IR) or aradio-frequency (RF) communication link. An example of a load controldevice able to transmit and receive digital messages on an RFcommunication link is described in commonly assigned U.S. Pat. No.5,905,442, issued May 18, 1999, entitled METHOD AND APPARATUS FORCONTROLLING AND DETERMINING THE STATUS OF ELECTRICAL DEVICES FROM REMOTELOCATIONS, the entire disclosure of which is hereby incorporated byreference.

FIG. 8A is a diagram of an example remote load control device of amultiple location load control system, e.g., the remote dimmer 504 ofthe load control system 500 shown in FIG. 5A. The remote dimmer 504 maycomprise one or more of the same functional blocks as the main dimmer502. The remote dimmer 504 may comprise a control circuit 814, azero-crossing detect circuit 816, an air-gap switch 822, amulti-location circuit 832, a power supply 830, the user interface 600,the memory 718, the audible sound generator 720, and/or thecommunication circuit 725.

The control circuit 814 may comprise a microcontroller, amicroprocessor, a programmable logic device (PLD), a field programmablegrid array (FPGA), an application specific integrated circuit (ASIC), orany suitable processing device, controller, or control circuit. Thecontrol circuit 814 may be coupled to a zero-crossing detect circuit816, which may determine the zero-crossing points of the AC line voltagefrom the AC power supply 506. The user interface 600 may be coupled tothe control circuit 814, such that the control circuit 814 is operableto receive inputs from the touch sensitive actuator 610 and to controlthe LEDs to provide feedback of the amount of power presently beingdelivered to the lighting load 508.

The remote dimmer 504 may comprise first and second hot terminals H1, H2that may be coupled in series with the controllably conductive device710 of the main dimmer 502, and may be adapted to conduct the loadcurrent from the AC power source 506 to the lighting load 508. Theremote dimmer 504 may also comprise an accessory dimmer terminal AD thatis adapted to be coupled to the accessory dimmer terminal AD of the maindimmer 502 via the AD line 509.

The power supply 830 may be coupled between the multi-location circuit832 and the first and second hot terminals H1, H2 to draw power from themain dimmer 502, via the multi-location circuit 832, during the chargingtime period T_(CHRG) of a half cycle. The power supply 830 may generatea DC output voltage V_(DD) (e.g., approximately 3.3 volts) for poweringthe control circuit 814 and other low voltage circuitry of the remotedimmer 504. The power supply 830 may comprise a capacitor 940, forexample, as shown in FIG. 9.

The zero-crossing detect circuit 816 may be coupled between theaccessory dimmer terminal AD and the first and second hot terminals H1,H2. The zero-crossing detect circuit 816 may detect a zero-crossingand/or may couple the AD supply voltage V_(AD) across the zero-crossingdetect circuit 816. The control circuit 814 may begin timing at azero-crossing (e.g., each zero-crossing) and may be operable to transmitand receive digital messages via the multi-location circuit 832, forexample, after the charging time period T_(CHRG) expires. Themulti-location circuit 832 may be coupled between the AD line 509 andthe power supply 830. The multi-location circuit 832 and power supply830 of the remote dimmer 504 may be coupled in parallel with themulti-location circuit 732 of the main dimmer 502 forming acommunication path during the communication time period T_(COMM) in thepositive and/or negative half cycles, for example, depending on whichside of the system 500/510 to which the main dimmer 502 is coupled.Accordingly, the communication path between the main dimmer 502 and theremote dimmer 504 may not pass through the AC power source 506 or thelighting load 508.

The opening of the air-gap switch 822 of the remote dimmer 504 mayprovide a true air-gap disconnect between the AC power source 506 andthe lighting load 508. The zero-crossing detect circuit 816, the powersupply 830, and the multi-location circuit 832 of the remote dimmer 504may include diodes coupled to the accessory dimmer terminal AD, suchthat the accessory dimmer terminal AD of the remote dimmer 504 may beoperable (e.g., only operable) to conduct current into the remote dimmer504. The path for leakage current through the system 500 may be throughthe dimmed hot terminal DH and out of the accessory dimmer terminal ADof the main dimmer 502. The orientation of the first and second hotterminals H1 and H2 of the remote dimmer 504 with respect to the maindimmer 502 may be reversed, for example, such that the second hotterminal H2 of the remote dimmer 504 may be coupled to the dimmed hotterminal DH of the main dimmer 502 and the first hot terminal H1 of theremote dimmer 504 may be coupled to the lighting load 508. This may beperformed to the path for leakage current to the lighting load 508through the accessory dimmer terminal AD of the remote dimmer 504. Thecomponents chosen for these circuits may be such that the magnitude ofthe leakage current through the main dimmer 502 is limited to anappropriate level to meet the UL standard for leakage current when theair-gap switch 722 is opened.

When any of the main dimmer 502 and the remote dimmers 504 are wireddirectly to the AC power source 506 and the lighting load 508, therespective air-gap switches 722, 822 may be positioned towards the ACpower source and the lighting load, such that opening the air-gapswitches 722, 822 may provide a true air-gap disconnect between the ACpower source 506 and the lighting load 508. However, if any of the maindimmer 502 and the remote dimmers 504 that are wired directly to the ACpower source 506 and the lighting load 508 do not have their air-gapswitches 722, 822 positioned towards the AC power source 506 and thelighting load 508, the leakage current through the main dimmer 502 andthe remote dimmers 504 may be limited to meet the UL standard forleakage current when an air-gap switch is opened. The leakage currentmay be limited in this way when the air-gap switches 722, 822 of any ofthe remote dimmers 504 that are wired in the middle of the system 500are opened.

FIG. 8B is a diagram of another example remote load control device of amultiple location load control system, e.g., the remote dimmer 514 ofthe load control system 510 shown in FIG. 5B. The remote dimmer 514 maycomprise one or more of the same functional blocks as the remote dimmer504. The remote dimmer 514 may comprise a control circuit 814, azero-crossing detect circuit 816, a multi-location circuit 832, a powersupply 830, the user interface 600, the memory 718, the audible soundgenerator 720, and/or the communication circuit 725. One or more of theembodiments described herein with reference to the remote dimmers 504(e.g., those associated with FIG. 9-18) may be applicable to the remotedimmers 514.

The remote dimmer 514 may not comprise an air-gap switch 822. As such,the remote dimmer 514 may comprise a single hot terminal H′ as opposedto the first and second hot terminals H1 and H2. The single hot terminalH′ of the remote dimmer 514 may be connected to the dimmed hot terminalDH of the main dimmer 502 and to the lighting load 508 (e.g., and thesingle H terminal of one or more additional remote dimmers 514), forexample, as illustrated in FIG. 5B. Alternatively, the single hotterminal H′ may be connected to the hot terminal H of the main dimmer502 and the AC power source 506, for example, if the main dimmer 502 iswired to the line side. The single hot terminal H′ of the remote dimmer514 may be coupled to the controllably conductive device 710 of the maindimmer 502, for example, via the H or DH terminal. The remote dimmer 514may not be adapted to conduct the load current from the AC power source506 to the lighting load 508, since for example, the DH terminal of themain dimmer 502 may be connected directly to the lighting load 508(e.g., without traveling through the remote dimmer 514). The accessorydimmer terminal AD of the remote dimmer 514 may be adapted to be coupledto the accessory dimmer terminal AD of the main dimmer 502 via the ADline 509.

FIG. 9 is an example schematic diagram of a multi-location circuit and acontrol circuit, e.g., the multi-location circuit 732 and controlcircuit 714 of the main dimmer 502, and/or the multi-location circuit832 and control circuit 814 of the remote dimmer 504 and/or the remotedimmer 514. Although described with respect to the remote dimmer 504,the description of FIG. 9 may be applicable to the remote dimmer 514,either entirely or in part. The main dimmer 502 may be connected to theremote dimmers 504 via the AD line 509 and the traveler line 511. Thetraveler line 511 may be connected between the hot terminal or dimmedhot terminal of the main dimmer 502 and one of the hot terminals of theremote dimmer 504, for example, depending on whether the main dimmer 502is configured on the line side or the load side of the system 500. Themain dimmer 502 may communicate (i.e., transmit and receive digitalmessages) and deliver power to a remote dimmer 504 via the AD line 509.

The multi-location circuit 732 of the main dimmer 502 may comprise anNPN bipolar junction transistor Q906, an NPN bipolar junction transistorQ908, an NPN bipolar junction transistor Q910, an NPN bipolar junctiontransistor Q912, a capacitor 918, a diode D920, a resistor R922, aresistor R924, and/or a resistor R926. The control circuit 714 of themain dimmer 502 may comprise a universal asynchronousreceiver/transmitter (UART) 928 and/or an NPN bipolar junctiontransistor Q916. The UART 928 may be an internal circuit of amicroprocessor of the control circuit 714.

The collector of the transistor Q906 may be connected to the hotterminal of the main dimmer 502. The emitter of the transistor Q906 maybe connected to the non-isolated circuit common and may be connected tothe collector of the transistor Q908 through the capacitor 918. Thecollector of the transistor Q908 may be connected to the non-isolatedcircuit common through the capacitor 918 and the emitter of thetransistor Q908 may be connected to the AD line 509 through the diodeD920. The base of the transistor Q908 may be connected to the transmitnode of the UART 928. The collector of the transistor Q910 may beconnected to the AD line 509 and the emitter of the transistor Q910 maybe connected to the non-isolated circuit common through the resistorsR922, R924. The junction of the resistors R922, R924 may be coupled tothe receive node (Rx) of the UART 928. The collector of the transistorQ912 may be connected to the AD line 509 and the emitter of thetransistor Q912 may be connected to the non-isolated circuit commonthrough the resistor R926.

The multi-location circuit 732 of the remote dimmer 504 may comprise anNPN bipolar junction transistor Q930, an NPN bipolar junction transistorQ932, an NPN bipolar junction transistor Q934, a diode D942, a resistorR944, a resistor R946, and/or a resistor R948. The control circuit 814of the remote dimmer 504 may comprise a universal asynchronousreceiver/transmitter (UART) 950 and an NPN bipolar junction transistorQ936. The remote dimmer 504 may comprise a capacitor 940, which may becoupled across the input of the power supply 830 of the remote dimmer504. As such, the capacitor 940 may be coupled between themulti-location circuit 832 and a hot terminal H1/H2/H′ to charge throughthe diode D942 from the main dimmer 502, via the multi-location circuit832, during the charging time period T_(CHRG) of a half cycle. The powersupply 830 may conduct current from the main dimmer 502 and/or from thecapacitor 940 to generate the DC supply voltage V_(DD) for powering thecontrol circuit 1114 and other low voltage circuitry of the remotedimmer 504.

The collector of the transistor Q930 may be connected to the AD line 509and the emitter of the transistor Q930 may be connected to thenon-isolated circuit common through the resistor R944. The collector ofthe transistor Q932 may be connected to the AD line 509 and the emitterof the transistor Q932 may be connected to the non-isolated circuitcommon through the resistors R946, R948. The junction of the resistorsR946, 948 may be coupled to the receive node (Rx) of the UART 950. Thecollector of the transistor Q934 may be connected to the capacitor 940and the emitter of the transistor Q934 may be connected to the AD line509. The base of the transistor Q934 may be connected to the transmitnode of the UART 950.

The main dimmer 502 and/or the remote dimmer 504 may control the AD line509 using tri-state logic. Tri-state logic may be referred to astri-state communication, three-state logic, 3-state logic, and/or thelike. The sender (e.g., the main dimmer 502 or the remote dimmer 504)may controlling the AD line 509 into one of three states, an activepull-up state, and active pull-down state, or a high impedance state.The main dimmer 502 and/or the remote dimmer 504 may control the AD line509 using tri-state logic to, for example, charge a power supply (e.g.,capacitor 940) of the remote dimmer 504 and/or communicate with oneanother.

The main dimmer 502 may charge the capacitor 940 of the remote dimmer504 during a half cycle of an AC voltage waveform (e.g., as shown inFIG. 10A) using the AD line 509. The main dimmer 502 may actively pullup the AD line 509 to generate an AD supply voltage VAD on the AD line509 during the changing time period T_(CHRG). In the active pull-upstate, the potential between the AD line 509 and the traveler line 511may vary between approximately 80 to 170 volts. To pull up the AD line509 during the charging time period T_(CHRG), the transistor Q906 andthe transistor Q908 of the main dimmer 502 may be rendered conductive,while the transistor Q910 and the transistor Q912 of the main dimmer502, and the transistor Q930, the transistor Q932, and the transistorQ934 of the remote dimmer 504 may be rendered non-conductive. As such, acurrent from the AC power source 506 may be conducted through thetransistor Q906 to charge the capacitor 918 of the main dimmer 502. Inaddition, a charging current may be conducted from the capacitor 918through the transistor Q908, the diode D920, the AD line 509, and thediode D942 to charge the capacitor 940 of the remote dimmer 504.Therefore, the capacitor 940 of the remote dimmer 504 may be charged bythe main dimmer 502 via the AD line 509, and the multi-location circuit832 and the power supply 830 may generate the DC supply voltage V_(DD).Residual current from the AC power source 506 provided after thecapacitor 940 is fully charged may return via the traveler wire 511.

The main dimmer 502 and the remote dimmer 504 may communicate during ahalf cycle of an AC voltage waveform (e.g., as shown in FIG. 10A) usingthe AD line 509. For example, the main dimmer 502 may charge thecapacitor 940 of the remote dimmer 504, and the main dimmer 502 and theremote dimmer 504 may communicate at least a portion of a digitalmessage during a single half cycle of an AC voltage waveform.

The main dimmer 502 and the remote dimmers 504 may communicate with oneanother by controlling the AD line 509. For example, the main dimmer 502and/or the remote dimmer 504 may communicate by placing the AD line 509in an active pull-up state and/or an active pull-down state. Thereceiver (e.g., the main dimmer 502 or the remote dimmer 504) mayinterpret a “1” bit when the AD line 509 is in the active pull-up state,a “0” bit when the AD line 509 is in the active pull-down state, andnothing when the AD line 509 is in the high impedance state. In theactive pull-up state, the potential between the AD line 509 and thetraveler wire 511 may vary between approximately 80 to 170 volts. In theactive pull-down state, there may be no potential between the AD line509 and the traveler wire 511. In the high impedance state, thepotential between the AD line 509 and the traveler wire 511 may dependon the charge stored by the line capacitance of the electrical wiringbetween the main dimmer 502 and the remote dimmer 504, i.e., the AD line509. The use of the active pull-up state and active pull-down state mayallow for faster and/or more reliable communication, for example,because the active pull-up state and active pull-down state may becharacterized by sharper edges between communications.

When the main dimmer 502 is transmitting a digital message to the remotedimmer 504, the transistor Q906 of the main dimmer 502 may be renderedconductive. To receive a digital message from the main dimmer 502, theremote dimmer 504 may render the transistor Q932 conductive (e.g., viathe Rx Enable line at the base of the transistor Q932). To place the ADline 509 in the active pull-up state, the main dimmer 502 may render thetransistor Q908 conductive and the transistor Q912 non-conductive. Assuch, the AD line 509 is pulled up (i.e., pulled-up to approximately80-170 volts) and the remote dimmer 504 (i.e., the UART 950 of thecontrol circuit 814) interprets a “1” bit being communicated. To placethe AD line 509 in the active pull-down state, the main dimmer 502 mayrender the transistor Q908 non-conductive and the transistor Q912conductive. As such, the AD line 509 is pulled down and hassubstantially the same voltage potential as the traveler wire 511. Whenthe AD line 509 is pulled-down, the remote dimmer 504 interprets a “0”bit being communicated. For example, the transistor Q912 may be renderedconductive (e.g., only rendered conductive) to transmit a “0” bit.Therefore, the main dimmer 502 may render a first switching circuit(e.g., transistor Q908) and a second switching circuit (e.g., transistorQ912) conductive and non-conductive on a complementary basis to transmita digital message to the remote dimmer 504 via the AD line 509 duringthe communication period T_(COMM) of the half cycle of the AC powersource. For example, during communication, the main dimmer 502 mayactively pull-up or pull-down the AD line 509 to communicate a “1” bitor a “0” bit, respectively, by rendering the transistors Q908, Q912conductive or non-conductive on a complementary basis.

When the remote dimmer 504 is transmitting a digital message to the maindimmer 502, the transistor Q934 of the remote dimmer 504 may be renderedconductive. To receive a digital message from the remote dimmer 504, themain dimmer 502 may render the transistor Q910 conductive (e.g., via theRx Enable line at the base of the transistor Q910). To place the AD line509 in the active pull-up state, the remote dimmer 504 may render thetransistor Q934 conductive and the transistor Q930 non-conductive. Assuch, the AD line 509 is pulled up (i.e., pulled-up to approximately80-170 volts) and the main dimmer 502 (i.e., the UART 928 of the controlcircuit 714) interprets a “1” bit being communicated. To place the ADline 509 in the active pull-down state, the remote dimmer 504 may renderthe transistor Q934 non-conductive and the transistor Q930 conductive.As such, the AD line 509 is pulled down and has substantially the samevoltage potential as the traveler wire 511. When the AD line 509 ispulled-down, the main dimmer 502 interprets a “0” bit beingcommunicated. For example, the transistor Q930 may be renderedconductive (e.g., only rendered conductive) to transmit a “0” bit.Therefore, the remote dimmer 504 may render a first switching circuit(e.g., transistor Q934) and a second switching circuit (e.g., transistorQ930) conductive and non-conductive on a complementary basis to transmita digital message to the main dimmer 502 via the AD line 509 during thecommunication period T_(COMM) of the half cycle of the AC power source.For example, during communication, the remote dimmer 504 may activelypull-up or pull-down the AD line 509 to communicate a “1” bit or a “0”bit, respectively, by rendering the transistors Q930, Q934 conductive ornon-conductive on a complementary basis.

The main dimmer 502 and the remote dimmer 504 may attempt to transmitdigital messages at the same time. If the main dimmer 502 and the remotedimmer 504 both attempt to transmit the same bit at the same time (e.g.,by both placing the AD line 509 in the active pull-up state or theactive pull-down state), neither device will be able to determine thatthe other device is also trying to transmit a digital message. However,if the main dimmer 502 and the remote dimmer 504 attempt to transmitdifferent bits at the same time, one device may “win” and the devicethat lost will stop transmitting the digital message. For example, thedevice that transmitted a “1” bit (e.g., a pull-up state) may win andthe device that transmitted a “0” bit (e.g., a pull-down state) maydetect that the other device transmitted the “1” bit and stoptransmitting the digital message. In other words, if the main dimmer 502attempts to place the AD line 509 in the active pull-down state and theremote dimmer 504 attempts to place the AD line 509 in the activepull-up state at the same time, the AD line 509 may be pulled up (e.g.,pulled up to approximately 80-170 volts) and the main dimmer 502 may beable to determine that the remote dimmer 504 placed the AD line 509 inthe active pull-up state. Similarly, if the remote dimmer 504 attemptsto place the AD line 509 in the active pull-down state and the maindimmer 502 attempts to place the AD line 509 in the active pull-up stateat the same time, the AD line 509 may be pulled up and the remote dimmer504 may be able to determine that the main dimmer 502 placed the AD line509 in the active pull-up state. In addition, the device thattransmitted a “0” bit may win and the device that transmitted a “1” bitmay detect that the other device transmitted the “0” bit and stoptransmitting the digital message (e.g., in a weak pull-up scheme, and inalternative to a strong pull-up scheme where the pull-up state isstronger than the pull-down state). Even though the losing device maystop transmitting the digital message, the losing device may still beable to receive the digital message transmitted by the winning deviceand/or may transmit a digital message to request for the winning deviceto retransmit the previous digital message.

The AD line 509 may be placed in the high impedance state. To place theAD line 509 in the high impedance state, the transistor Q906 may berendered conductive and the transistors Q908, Q910, and Q912 of the maindimmer 502 and the transistors Q930, Q932, and Q934 of the remote dimmermay be rendered non-conductive. As such, in the high impedance state,the potential between the AD line 509 and the traveler wire 511 maydepend on the charge stored by the AD line 509. The interpretation ofthe AD line 509 by the receiver (e.g., the main dimmer 502 or the remotedimmer 504) in the high impedance state is indeterminable. Themulti-location circuits 732, 832 dissipate less power in the highimpedance state.

In the multi-location circuit 732, the Pull-down line 960 of thetransistor Q912 may be the inverted version of the Tx_control line 962at the base of the transistor Q908. For example, an inverter circuit(not shown) may be located between the base of the transistor Q912(i.e., on the Pull-down line 960) and the base of the transistor Q908(i.e., on the Tx_control line 962). The Pull-down line 960 also may becoupled (not shown) to the control circuit 714 (e.g., to an open drainoutput of a microprocessor), so that the control circuit 714 may pulldown the base of the transistor Q912 to render the transistor Q912non-conductive during the high impedance state (i.e., to disable controlof the transistor Q912 in response to the Pull-down line 960). Thetransistor Q912 may be rendered conductive (e.g., only renderedconductive) when the transistor Q908 is rendered non-conductive duringthe communication time.

In the multi-location circuit 832, the Pull-down line 968 of thetransistor Q930 may be the inverted version of the Tx_control line 966at the base of the transistor Q934. For example, an inverter circuit(not shown) may be located between the base of the transistor Q930(i.e., on the Pull-down line 968) and the base of the transistor Q934(i.e., on the Tx_control line 966). The Pull-down line 968 may becoupled (not shown) to the control circuit 814 (e.g., to an open drainoutput of a microprocessor), so that the control circuit 814 may pulldown the base of the transistor Q930 to render the transistor Q930non-conductive during the high impedance state (i.e., to disable controlof the transistor Q912 in response to the Pull-down line 968). Thetransistor Q930 may be rendered conductive (e.g., only renderedconductive) when the transistor Q934 is rendered non-conductive duringthe communication time.

FIG. 10A is a timing diagram of an example of a complete line cycle ofan AC voltage waveform 1000 provided by an AC power source (e.g., the ACpower source 506). The timing diagram of FIG. 10A illustrates an exampleof the operation of a main dimmer 502 during each half cycle of the ACvoltage waveform 1000. The main dimmer 502 may be operable to allow oneor more remote dimmers 504 connected to the AD line 509 to charge theirinternal power supplies (i.e., capacitor 940) during a charging timeperiod T_(CHRG). The charging time period T_(CHRG) may occur after azero-crossing 1002 at the beginning of the positive half cycle of the ACvoltage waveform 1000. The charging time period T_(CHRG) may beapproximate 2 ms in duration. The AD line 509 may be pulled up by themain dimmer 502 during the charging time period T_(CHRG) to charge thecapacitors 940 of the remote dimmers 504, for example, as described withreference to FIGS. 9.

After the charging time period T_(CHRG), a first buffer time T_(BUF1)may be used to ensure that the state of the AD line 509 during thecharging time period T_(CHRG) is not misinterpreted as part of a digitalmessage during the communication time period T_(COMM).

After the buffer time T_(BUF1), the main dimmer 502 and one or more ofthe remote dimmers 504 may be operable to transmit and receive digitalmessages via the AD line 509 during the communication time periodT_(COMM). The communication time period T_(COMM) may occur after thebuffer time T_(BUF1) and during the positive half cycle of the ACvoltage waveform 1000. The communication time period T_(COMM) may beapproximate 3.75 ms. The communication time period T_(COMM) may be adedicated time slot for communication between the main dimmer 502 andone or more remote dimmers 504. The main dimmer 502 and/or a remotedimmer 504 may pull up and/or pull down the AD line 509 to transmit adigital message, for example, as described with reference to FIG. 9. Assuch, communication between the main dimmer 502 and one or more remotedimmers 504 may be performed during the communication time periodT_(COMM) using the active pull-up state and/or the active pull-downstate. After the communication time period T_(COMM), the AD line 509 maybe in a high impedance state (i.e., the high impedance state).

The remote dimmer 504 may monitor for the beginning of a charge pulseduring a charge pulse window T_(CPW) right before the next zero-crossing1006. The charge pulse may occur during the charging time periodT_(CHRG) each line cycle. The charge pulse window T_(CPW) may beginafter a charge pulse window delay period T_(DELAY), which may have aduration of approximately 14 ms measured from the zero-crossing 1002.The charge pulse window T_(CPW) may begin at a time 1005 before thezero-crossing 1006 between the negative half cycle of the AC voltagewaveform 1000 and a subsequent cycle of the AC voltage waveform 1000,for example, as shown in FIG. 10A. During the charge pulse windowT_(CPW), the remote dimmers 504 may open their charge pulse detectwindow, which may be used by the remote dimmers 504 to stay insynchronization with the main dimmer 502. For example, the rising edgeof the charge pulse during the charging time period T_(CHRG) may bedetected by the zero-cross detect circuit 816 to establish the timingfor the rest of the line cycle. The AD line 509 may be in a highimpedance state (i.e., the high impedance state) during the charge pulsewindow T_(CPW).

Although illustrated as comprising the charging time period T_(CHRG) andthe communication time period T_(COMM) during the positive half cycle ofthe AC voltage waveform 1000 but not the negative half cycle of the ACvoltage waveform 1000, in one or more embodiments, the AC voltagewaveform 1000 may include a charging time period T_(CHRG) and acommunication time period T_(COMM) during the negative half cycle of theAC voltage waveform 1000 but not the positive half cycle of the ACvoltage waveform 1000.

When the lengths of the electrical wires between the main dimmer 502 andthe remote dimmer 504 are long, the capacitance between the AD line 509and the traveler wire 511 may have a large magnitude. In addition, thecapacitance between the AD line 509 and the neutral wiring 512 and thecapacitance between the traveler wire 511 and the neutral wiring 512 mayhave large magnitudes (e.g., if the main dimmer 502 has a neutralterminal coupled to the neutral wiring 512 that is bundled with the ADline 509 and the neutral wiring 512). If the charge stored by thecapacitance between the AD line 509 and the traveler wire 511 rises toohigh when the AD line 509 is in the high impedance state, the maindimmer 502 and/or the remote dimmer 504 may incorrectly determine thatthe AD line 509 in the active pull-up state, which can causecommunication errors (e.g., since a “1” bit wins over a “0” bit). Forexample, large voltages may be produced between the AD line 509 and thetraveler wire 511 (e.g., and/or between these lines and the neutralwiring 512) when the control circuit 714 is controlling the controllablyconductive device 710 using the reverse phase control technique and thelengths of the electrical wires between the main dimmer 502 and theremote dimmer 504 are long.

FIG. 10B is a timing diagram of example waveforms illustrating theoperation of the main dimmer 502 when using the reverse phase controldimming technique. FIG. 10B shows an example phase control waveform 1010generated by the controllably conductive device 710 when the controlcircuit 714 is using the reverse phase control technique. When thecontrol circuit 714 is controlling the controllably conductive device710 using the reverse phase control dimming technique, the controlcircuit may render the controllably conductive device 710 conductive atapproximately the beginning of a half cycle (e.g., at zero-crossing1002). The control circuit 714 may then render the controllablyconductive device 710 non-conductive at a transition time t_(TRAN)during the half cycle, such that the controllably conductive device 710is conductive for a conduction time T_(CON) at the beginning of eachhalf cycle and non-conductive for a non-conduction time T_(NC) at theend of each half cycle. The control circuit 714 may be configured togenerate a drive signal 1012 that may be provided to the gate drivecircuit 712 for rendering the controllably conductive device 710conductive and non-conductive. The control circuit 714 may vary thetransition time t_(TRAN) and thus the length of the conductive periodT_(CON) to control the amount of power delivered to the load.

When the controllably conductive device 710 is rendered non-conductiveand the AD line 509 is in the high impedance state, the capacitancebetween the AD line 509 and the traveler wire 511 may be able to chargeto a voltage that is high enough to cause a communication error duringthe communication time period T_(COMM) in the positive half cycles.Accordingly, when the control circuit 714 is controlling thecontrollably conductive device 710 using the reverse phase controldimming technique, the control circuit 714 may be configured to controlthe AD line 509 to the active pull-down state for a blanking time periodT_(BL) around the transition time T_(TRAN) when the controllablyconductive device 710 is rendered non-conductive. The control circuitmay 714 be configured to control the AD line 509 to the active pull-downstate for the blanking time period T_(BL) around the transition timeT_(TRAN) when the controllably conductive device 710 is renderednon-conductive during the position half cycles (e.g., and/or duringnegative half cycles if the main dimmer 502 and the remote dimmer 504communicate during the negative half cycles). The blanking time periodT_(BL) may begin at approximately the same time as the transition timeT_(TRAN). The control circuit 714 may generate a pull-down signal 1014on the pull-down line 960 to render the transistor Q912 of themulti-location circuit 732 conductive at approximately the same time asrendering the controllably conductive device 710 non-conductive eachhalf cycle. The control circuit 714 may render the transistor Q912conductive to place the AD line 509 in the active pull-down state forthe length of the blanking time period T_(BL) around the transition timeT_(TRAN) each half cycle (e.g., if no remote control devices 504 areattempting to place the AD line in the active pull-up state). During theblanking time period T_(BL), the transistor Q912 may provide a path forthe capacitance between the AD line 509 and the traveler wire 511 todischarge. The length of the blanking time period T_(BL) may be longenough to discharge the capacitance between the AD line 509 and thetraveler wire 511 (e.g., approximately 50-200 microseconds). Theblanking time period T_(BL)may also begin before the transition timeT_(TRAN) (e.g., 10-20 microseconds before the transition time T_(TRAN))and end after the transition time T_(TRAN).

While the control circuit 714 is rendering the transistor Q912conductive (e.g., and placing the AD line 509 in the active pull-downstate for the length of the blanking time period T_(BL)), the controlcircuit can determine if the remote dimmer 504 placed the AD line 509 inthe active pull-up state and is transmitting a digital message, forexample, because the pull-up state may be stronger than the pull-downstate (e.g., a “1” bit may win over a “0” bit). Accordingly, the controlcircuit 714 may still be able to receive a digital message from theremote dimmer 504 while attempting to place the AD line in the activepull-down state during the blanking time period T_(BL). In addition, thecontrol circuit 714 may be configured to transmit a digital message torequest for the remote dimmer 504 to retransmit the previous digitalmessage in response to detecting that the remote dimmer 504 transmitteda digital message while the main dimmer 502 was attempting to place theAD line in the active pull-down state during the blanking time periodT_(BL).

As previously mentioned, the main dimmer 502 and the remote dimmer 504may communicate such that a “0” bit wins over a “1” bit. In addition,the control circuit 714 may also control the controllably conductivedevice 710 using the forward phase control technique. When the controlcircuit 714 is controlling the controllably conductive device 710 usingthe forward phase control dimming technique, the control circuit may notrender the controllably conductive device 710 conductive atapproximately the beginning of a half cycle, but may render thecontrollably conductive device 710 conductive at the transition timet_(TRAN) during the half cycle, such that the controllably conductivedevice 710 is non-conductive for a non-conduction time T_(NC) at thebeginning of each half cycle and conductive for a conduction timeT_(CON) at the end of each half cycle and. The control circuit 714 mayvary the transition time t_(TRAN) and thus the length of the conductiveperiod T_(CON) to control the amount of power delivered to the load.

When the control circuit 714 is controlling the controllably conductivedevice 710 using the forward phase control dimming technique, thecapacitance between the traveler wire 511 and the AD line 509 may chargethe traveler wire 511 and the AD line 509. When the controllablyconductive device 710 is rendered conductive and the AD line 509 is inthe high impedance state, the capacitance between the traveler wire 511and the AD line 509 may be able to charge to a voltage that is highenough that the main dimmer 502 and/or the remote dimmer 504 mayincorrectly determine that the AD line 509 in the active pull-down stateduring the communication time period T_(COMM), which can causecommunication errors since a “0” bit may win over a “1” bit (e.g., in aweak pull-up scheme).

Accordingly, when the control circuit 714 is controlling thecontrollably conductive device 710 using the forward phase controldimming technique, the control circuit may be configured to control theAD line 509 to the active pull-up state for a blanking time periodT_(BL) around the transition time T_(TRAN) when the controllablyconductive device 710 is rendered conductive during the positive halfcycles. The blanking time period T_(BL) may begin at approximately thesame time as the transition time t_(TRAN). The control circuit 714 mayrender the transistor Q908 of the multi-location circuit 732 conductiveat approximately the same time as rendering the controllably conductivedevice 710 conductive each half cycle to compensate for the negativecharge between the AD line 509 and the traveler wire 511.

FIG. 11 is a diagram of an example of a payload format for communicationbetween the main dimmer 502 and the remote dimmer 504, 514. A packet1100 may comprise two frames. The first frame may comprise a framenumber 1102 and event data 1104. The second frame may comprise a framenumber 1106, event type 1108, device address 1110, and an errordetection 1112. The frame number field 1102 and the frame number field1106 may identify which frame of the packet 1100 is being sent. Theframe number 1102 and the frame number 1106 may comprise one bit each.The event data 1104 may comprise the data being communicated between themain dimmer and the remote dimmer. The event data 1104 may comprisefifteen bits. The event type 1108 may indicate the type of packet 1100communicated via the AD line 509. For example, the event type 1108 mayencode the possible packet types that will be communication via the ADline 509. The event type 1108 may comprise seven bits. The deviceaddress 1110 may identify the source device of the packet 1100. Thedevice address 1110 may comprise three bits. The error detection field1112 may encode the forward error detection result to be used by thereceiving device to validate the packet 1100. For example, the errordetection field 1112 may comprise a multi-bit cyclic redundancy check(CRC) (e.g., a five bit CRC) that may be used by the receiving device tovalidate the packet 1100.

FIG. 12 is a flowchart of an example of a user interface procedure 1700executed periodically by the control circuit 714 of the main dimmer 502,e.g., once every 10 msec. The user interface procedure 1700 mayselectively execute one of three routines depending upon the state ofthe main dimmer 502. If the main dimmer 502 is in an “Idle” state (i.e.,the user is not actuating the touch sensitive actuator 610) at step1710, the control circuit 714 may execute an Idle routine 1800. If themain dimmer 502 is in an “ActiveHold” state (i.e., the user is presentlyactuating the touch sensitive actuator 610) at step 1720, the controlcircuit 714 may execute an ActiveHold routine 1900. If the main dimmer502 is in a “Release” state (i.e., the user has recently ceasedactuating the touch sensitive actuator 610) at step 1730, the controlcircuit 714 may execute a Release routine 2000.

FIG. 13 is a flowchart of an example of the Idle routine 1800, which maybe executed periodically when the main dimmer 502 is in the Idle state.The control circuit 714 may change the state of the main dimmer 502 tothe ActiveHold state when the user actuates the touch sensitive actuator610. For example, if there is activity on the touch sensitive actuator610 of the main dimmer 502 at step 1810, an activity counter may beincremented at step 1812. Otherwise, the activity counter may be clearedat step 1814. The activity counter may be used by the control circuit714 to ensure that the main dimmer 502 changes to the ActiveHold state(e.g., only changes to the ActiveHold state) in response to an actuationof the touch sensitive actuator 610 and not as a result of noise or someother undesired impulse. The use of the activity counter may be similarto a software “debouncing” procedure for a mechanical switch. If theactivity counter is not less than a maximum activity counter valueA_(MAX) at step 1816, then the state of the main dimmer 502 is set tothe ActiveHold state at step 1818. Otherwise, the Idle routine 1800 mayexit.

FIG. 14 is a flowchart of an example of the ActiveHold routine 1900,which may be executed once every half cycle when the touch sensitiveactuator 610 is being actuated, i.e., when the main dimmer 502 is in theActiveHold state. The control circuit 714 may make a determination as towhether the user has stopped using, i.e., released, the touch sensitiveactuator 610. If there is no activity on the touch sensitive actuator610 at step 1910, the control circuit 714 may increment an “inactivitycounter” at step 1912. The control circuit 714 may use the inactivitycounter to make sure that the user is not still actuating the touchsensitive actuator 610 before entering the Release mode. If theinactivity counter is less than a maximum inactivity counter valueI_(MAX) at step 1914, the ActiveHold routine 1900 may exit. Otherwise,the state of the main dimmer 502 may be set to the Release state at step1915, and the routine 1900 may exit.

If there is activity on the touch sensitive actuator 610 at step 1910,the control circuit 714 may generate an audible sound at step 1916 usingthe audible sound generator 718. An example of the generation of theaudible sound is described in greater detail in co-pendingcommonly-assigned U.S. Pat. No. 7,608,948, issued Oct. 27, 2009,entitled TOUCH SCREEN WITH SENSORY FEEDBACK, the entire disclosure ofwhich is hereby incorporated by reference. The control circuit 714 maydetermine where along the length of the actuation member 612 that thetouch sensitive actuator is being actuated at step 1918. If the touchsensitive actuator 610 is being actuated in the toggle area, i.e., thelower portion 612B of the actuation member 612, at step 1920, thecontrol circuit 714 may process the actuation of the touch sensitiveactuator as a toggle. If the lighting load 508 is presently off at step1922, the control circuit 714 may turn the lighting load on. Forexample, the control circuit 714 may illuminate the lower portion 612Bof the actuation member 612 white at step 1924 and dim the lighting load508 up to the preset level, i.e., the desired lighting intensity of thelighting load, at step 1926. Further, the control circuit 714 may load adigital message into the TX buffer at step 1928. The message descriptionof the digital message may comprise, for example, a light level commandand the message data comprises the preset level.

If the lighting load is presently on at step 1922, the control circuit714 illuminates the lower portion 612B of the actuation member 612orange at step 1932 and controls the lighting load 508 to off at step1934. At step 1928, the control circuit 714 loads a digital message intothe TX buffer, where the message description is a light level commandand the message data comprises zero percent (or off).

If the touch sensitive actuator 610 is not being actuated in the togglearea at step 1920, the upper portion 612A is being actuated and thelocation of the actuation on the touch sensitive actuator 610 isrepresentative of the desired intensity level of the lighting load 508.At step 1936, the control circuit 714 may illuminate the upper portion612A of the actuation member 612 appropriately, i.e., as a bar graphrepresentative of the present intensity of the lighting load 508. Thecontrol circuit 714 may dim the lighting load 508 to the appropriatelevel as determined from the location of the actuation of the touchsensitive actuator 610 at step 1938. At step 1928, the control circuit714 loads the TX buffer with a digital message having a light levelcommand as the message description and the present intensity level asthe message data.

FIG. 15 is a flowchart of an example of the Release routine 2000, whichmay be executed after the control circuit 714 sets the state of thedimmer state to the Release state at step 1915 of the ActiveHold routine1900. The control circuit 714 may store the present intensity level ofthe lighting load 508 in the memory 718 at step 2010. At step 2012, thecontrol circuit 714 may store one or more entries of the last digitalmessage to be transmitted in response to the actuation of the touchsensitive actuator 610 into the TX buffer, for example, such that themain dimmer 502 may send one or more identical digital messages to theremote dimmers 504 to ensure that the remote dimmers received thedigital message. The control circuit 714 may set the state of the maindimmer 502 to the Idle state at step 2014, and the Release routine 2000may exit.

The message description of the digital messages transmitted between themain dimmer 502 and the remote dimmers 504 may comprise an advancedprogramming mode (APM) command, i.e., a command to adjust an advancedprogramming feature, such as a protected preset, a fade rate, and/or thelike. If an advanced programming mode feature is modified at the maindimmer 502, the main dimmer 502 may transmit to the remote dimmers 504 adigital message having the message description containing the APMcommand and the message data comprising the APM feature to change andthe value to change the APM feature to. For example, the digital messagemay be transmitted one or more times during the Release routine 2000. Anexample of an advanced programming mode is described in greater detailin commonly-assigned U.S. Pat. No. 7,190,125, issued Mar. 13, 2007,entitled PROGRAMMABLE WALLBOX DIMMER, the entire disclosure of which ishereby incorporated by reference.

FIG. 16 is a flowchart of an example of a RX buffer procedure 2100executed periodically by the control circuit 714 of the main dimmer 502,e.g., once every positive or negative half cycle. If there is a digitalmessage in the RX buffer at step 2110, the control circuit 714 maydetermine whether the message description of the digital messagecontains an APM command at step 2112 or a light level command at step2114. If the message description is an APM command at step 2112, the APMfeature is modified in the memory 718 at step 2116 and the procedure2100 exits. If the message description is a light level command at step2116 and the message data of the digital message is zero percent (i.e.,off) at step 2118, the control circuit 714 may illuminate the togglearea (i.e., the lower portion 612B of the actuation member 612) at step2120, and/or may control the lighting load 508 to off at step 2122. Onthe other hand, if the message data for the light level command is anintensity greater than zero percent at step 2118, the control circuit714 may illuminate the toggle area white at step 2124, and/or mayilluminate the upper portion 612A of the actuation member 612appropriately (i.e., as a bar graph representative of the presentintensity of the lighting load 508) at step 2126. The control circuit714 may control the intensity of the lighting load 508 to theappropriate level as determined from the message data of the digitalmessage at step 2128 and the procedure 2100 may exit.

FIG. 17 is a flowchart of an example of a multi-location controlprocedure 2200 executed by the control circuit 714 of the main dimmers502. The multi-location control procedure 2200 may be executedperiodically, e.g., once every line cycle. The procedure 2300 may beginat step 2210 when the zero-crossing detect circuit 716 signals azero-crossing to the control circuit 714 (e.g., at the beginning of thecharging time T_(CHRG) as shown in FIG. 10A). Upon receiving thezero-crossing signal, the control circuit 714 may start the chargingtime T_(CHRG) at step 2212. During the charging time T_(CHRG) at 2214,the main dimmer 502 may charge the power supply 830 of the remote dimmer504. For example, the control circuit 714 may render the transistorsQ906 and Q908 conductive to charge the capacitor 940 of the remotedimmer 504.

At 2216, the control circuit 714 may determine if the charging timeT_(CHRG) has ended. If not, then the control circuit 714 may continue tocharge the power supply 830 of the remote dimmer 504. If the chargingtime T_(CHRG) has ended, the control circuit 714 may start acommunication time T_(COMM) at 2218.

During the communication time T_(COMM), the control circuit 714 mayperform a communication routine at 2220. For example, the controlcircuit 714 may transmit a digital message to the remote dimmer 504and/or receive a digital message from the remote dimmer 504 via controlof the AD line 509 by the sender (i.e., placing the AD line 509 in theactive pull-up state and/or the active pull-down state). To transmit adigital message, the control circuit 714 may render the transistor Q906conductive. Then, to place the AD line 509 in the active pull-up stateto communicate a “1” bit, the control circuit 714 may render thetransistor Q908 conductive and the transistor Q912 non-conductive. Toplace the AD line 509 in the active pull-down state to communicate a “0”bit, the control circuit 714 may render the transistor Q908non-conductive and the transistor Q912 conductive. Therefore, thecontrol circuit 714 may inversely control the transistors Q908 and Q912in a complementary manner to communicate a “1” bit or a “0” bit. Toreceive a digital message from the remote dimmer 504 during thecommunication time T_(COMM), the control circuit 714 of the main dimmer502 may render the transistor Q910 conductive. During the communicationtime T_(COMM), the control circuit 714 may render the transistor 910conductive, such that the control circuit 714 is able to receive adigital message from the remote dimmer 504.

At 2222, the control circuit 714 may determine if the communication timeT_(COMM) has ended. If not, the control circuit 714 may continue toperform the communication routine. If the communication time T_(COMM)has ended, the control circuit 714 my place the AD line 509 in a highimpedance state at 2224, for example, until the next charging timeperiod T_(CHRG). For example, the control circuit 714 may render thetransistor Q906 conductive and the transistors Q908, Q910, and Q912non-conductive to place the AD line 509 in a high impedance state.

FIG. 18 is a flowchart of an example of a multi-location controlprocedure 2300 executed by the control circuit 814 of the remote dimmers504, 514. The multi-location control procedure 2300 may be executedperiodically, e.g., once every line cycle. The procedure 2300 may beginat step 2310 when the zero-crossing detect circuit 816 signals azero-crossing to the control circuit 814 (e.g., at the beginning of thecharging time T_(CHRG) as shown in FIG. 10A). Upon receiving thezero-crossing signal, the control circuit 814 may start the chargingtime T_(CHRG) at step 2312. During the charging time T_(CHRG) at 2314,the power supply 830 of the remote dimmer 504 may be charged by the maindimmer 502. For example, during the charging time T_(CHRG), the controlcircuit 814 may render the transistors Q930, Q932, and Q934non-conductive so that the capacitor 830 of the remote dimmer 504 may becharged.

At 2316, the control circuit 814 may determine if the charging timeT_(CHRG) has ended. If not, then the control circuit 814 may continue torender the transistors Q930, Q932, and Q934 non-conductive so that thepower supply 830 may be charged. If the charging time T_(CHRG) hasended, the control circuit 814 may start a communication time T_(COMM)at 2318.

During the communication time T_(COMM), the control circuit 814 mayperform a communication routine at 2320. For example, the controlcircuit 814 may transmit a digital message to the main dimmer 502 and/orreceive a digital message from the main dimmer 502 via control of the ADline 509 by the sender (i.e., placing the AD line 509 in the activepull-up state and/or the active pull-down state). To receive a digitalmessage, the control circuit 814 may render the transistor Q932conductive. To transmit a digital message, the control circuit 814 mayrender the transistor Q934 conductive. Then, to place the AD line 509 inthe active pull-up state to communicate a “1” bit, the control circuit814 may render the transistor Q934 conductive and the transistor Q930non-conductive. To place the AD line 509 in the active pull-down stateto communicate a “0” bit, the control circuit 814 may render thetransistor Q934 non-conductive and the transistor Q930 conductive.Therefore, the control circuit 814 of the remote dimmer 504 mayinversely control the transistors Q934 and Q930 in a complementarymanner to communicate a “1” bit or a “0” bit. During the communicationtime T_(COMM), the control circuit 814 may render the transistor 932conductive, such that the control circuit 814 is able to receive adigital message from the main dimmer 502.

At 2322, the control circuit 814 may determine if the communication timeT_(COMM) has ended. If not, the control circuit 814 may continue toperform the communication routine. If the communication time T_(COMM)has ended, the control circuit 814 my place the AD line 509 in a highimpedance state at 2324, for example, until the next charging timeperiod T_(CHRG). For example, the control circuit 814 may render thetransistors Q930, Q932, and Q934 non-conductive to place the AD line 509in a high impedance state.

At 2326, the control circuit 814 may determine if the window delayperiod T_(DELAY) is complete. If the delay period T_(DELAY) is complete,then the control circuit 814 may open the charge pulse window T_(CPW) at2328. During the charge pulse window T_(CPW), the control circuit 814may monitor for a charge pulse that may occur during a subsequentcharging time period T_(CHRG) during a subsequent line cycle. Thedetection of the charge pulse during the charge pulse window T_(CPW) maybe used by the control circuit 814 to stay in synchronization with themain dimmer 502. For example, the rising edge of the charge pulse duringthe charging time period T_(CHRG) may be detected by the zero-crossdetect circuit 816 to establish the timing for the rest of the linecycle. As such, the control circuit 814 may start a subsequent chargingtime T_(CHRG), e.g., return to 2312, upon detecting the charge pulse.

Since the digital messages transmitted between the main dimmers 502 andthe remote dimmers 504 may include APM commands, the APM features of theload control system 500/510 may be modified using the user interface 600of the main dimmer 502 and/or a remote dimmer 504. The main dimmer 502and the remote dimmers 504 may be used to adjust local advancedprogramming features (i.e., of the main dimmer 502) and global advancedprogramming features (i.e., affecting the main dimmer 502 and one ormore of the remote dimmers 504).

FIG. 19 is a flowchart of an example of a load control procedure 2400that may be executed by the control circuit 714 of the main dimmers 502for controlling the controllably conductive device 710 using the reversephase control technique. The load control procedure 2400 may be executedperiodically, e.g., once every line cycle. The load control procedure2400 may begin at step 2410 when the zero-crossing detect circuit 716signals a zero-crossing to the control circuit 714 (e.g., apositive-going zero-crossing at the beginning of the charging timeT_(CHRG) as shown in FIG. 10B). After receiving the zero-crossingsignal, the control circuit 714 may render the controllably conductivedevice 710 conductive at step 2412. If the transition time T_(TRAN) doesnot fall within the communication time period T_(COMM) during thepresent half cycle at step 2414, the control circuit 714 may render thecontrollably conductive device 710 non-conductive at the transition timeT_(TRAN) at step 2416 and the load control procedure 2400 may exit.

If the transition time T_(TRAN) falls within the communication timeperiod T_(COMM) at step 2414, but the control circuit 714 is presentlytransmitting a digital message at step 2418, the load control procedure2400 may simply exit. If the transition time T_(TRAN) falls within thecommunication time period T_(COMM) at step 2414 and the control circuit714 is not presently transmitting a digital message at step 2418, thecontrol circuit 714 may attempt to control the AD line 509 to the activepull-down state at step 2420 by rendering the transistor Q912 of themulti-location circuit 732 conductive at approximately the same time asthe transition time t_(TRAN). The control circuit 714 may then renderthe controllably conductive device 710 non-conductive at the transitiontime T_(TRAN) at step 2422 and control the AD line 509 to the highimpedance state at step 2424, before the load control procedure 2400exits. As shown in FIG. 19, the control circuit 714 may attempt tocontrol the AD line 509 before (e.g., immediately or slightly before)rendering the controllably conductive device 710 non-conductive at thetransition time T_(TRAN). In addition, the control circuit 714 mayattempt to control the AD line 509 after (e.g., immediately or slightlyafter) rendering the controllably conductive device 710 non-conductiveat the transition time T_(TRAN). The control circuit 714 may control theAD line 509 to the high impedance state at step 2424 by rendering thetransistor Q912 of the multi-location circuit 732 non-conductive at theend of the blanking time period T_(BL) (e.g., approximately 50-200microseconds from when the control circuit rendered the transistor Q912conductive).

Although described with reference to a main dimmer and a remote dimmer,one or more embodiments described herein may be used with other loadcontrol devices. For example, one or more of the embodiments describedherein may be performed by a variety of load control devices that areconfigured to control of a variety of electrical load types, such as,for example, a LED driver for driving an LED light source (e.g., an LEDlight engine); a screw-in luminaire including a dimmer circuit and anincandescent or halogen lamp; a screw-in luminaire including a ballastand a compact fluorescent lamp; a screw-in luminaire including an LEDdriver and an LED light source; a dimming circuit for controlling theintensity of an incandescent lamp, a halogen lamp, an electroniclow-voltage lighting load, a magnetic low-voltage lighting load, oranother type of lighting load; an electronic switch, controllablecircuit breaker, or other switching device for turning electrical loadsor appliances on and off; a plug-in load control device, controllableelectrical receptacle, or controllable power strip for controlling oneor more plug-in electrical loads (e.g., coffee pots, space heaters,other home appliances, and the like); a motor control unit forcontrolling a motor load (e.g., a ceiling fan or an exhaust fan); adrive unit for controlling a motorized window treatment or a projectionscreen; motorized interior or exterior shutters; a thermostat for aheating and/or cooling system; a temperature control device forcontrolling a heating, ventilation, and air conditioning (HVAC) system;an air conditioner; a compressor; an electric baseboard heatercontroller; a controllable damper; a humidity control unit; adehumidifier; a water heater; a pool pump; a refrigerator; a freezer; atelevision or computer monitor; a power supply; an audio system oramplifier; a generator; an electric charger, such as an electric vehiclecharger; and an alternative energy controller (e.g., a solar, wind, orthermal energy controller). A single control circuit may be coupled toand/or adapted to control multiple types of electrical loads in a loadcontrol system.

What is claimed is:
 1. A load control device for use in a load controlsystem for controlling an amount of power delivered from an AC powersource to an electrical load, the load control system comprising aremote control device adapted to be coupled to the load control devicevia an electrical wire, the load control device comprising: acontrollably conductive device adapted to be electrically coupled inseries between the AC power source and the electrical load; a controlcircuit configured to control the controllably conductive device tocontrol the amount of power delivered to the electrical load, thecontrol circuit configured to render the controllably conductive deviceconductive or non-conductive at a transition time during a half cycle ofthe AC power source; and a communication circuit adapted to be coupledto the electrical wire, the communication circuit configured to conducta charging current for a power supply of the remote control devicethrough the electrical wire, the communication circuit responsive to thecontrol circuit to control the electrical wire between an active pull-upstate and an active pull-down state to transmit a digital message to theremote control device via the electrical wire; wherein the controlcircuit is configured to control the communication circuit to generate ahigh impedance state on the electrical wire when the communicationcircuit is not transmitting a digital message to the remote controldevice, the control circuit further configured to control thecommunication circuit to provide the active pull-down state or theactive pull-up state on the electrical wire during a period of timearound the transition time of the controllably conductive device whenthe communication circuit is not transmitting a digital message to theremote control device.
 2. The load control device of claim 1, whereinthe communication circuit comprises a first switching circuit adapted tobe coupled between the AC power source and the electrical wire, thefirst switching circuit configured to conduct the charging current forthe power supply of the remote control device through the electricalwire during a charging time period of the half cycle of the AC powersource.
 3. The load control device of claim 2, wherein the communicationcircuit comprises a second switching circuit adapted to be coupledbetween the electrical wire and a circuit common, the control circuitconfigured to render the first switching circuit conductive and thesecond switching circuit non-conductive to generate the active pull-upstate, and to render the first switching circuit non-conductive and thesecond switching circuit conductive to generate the active pull-downstate, the control circuit configured to render the first and secondswitching circuits conductive and non-conductive on a complementarybasis to transmit the digital message to the remote control device viathe electrical wire during a second time period of the half cycle of theAC power source.
 4. The load control device of claim 3, wherein thecontrol circuit is configured to render the first and second switchingcircuits non-conductive to generate the high impedance state on theelectrical wire.
 5. The load control device of claim 4, wherein thecontrol circuit is configured to generate the high impedance state onthe electrical wire outside of the first and second periods of the halfcycle of the AC power source.
 6. The load control device of claim 3,wherein the first and second time periods occur during the positive halfcycles of the AC power source.
 7. The load control device of claim 6,wherein the control circuit is configured to control the communicationcircuit to provide the active pull-down state or the active pull-upstate on the electrical wire during the period of time around thetransition time of the controllably conductive device when thecommunication circuit is not transmitting a digital message to theremote control device during the positive half cycles of the AC powersource.
 8. The load control device of claim 1, wherein the controlcircuit is configured to control the controllably conductive device tocontrol the amount of power delivered to the electrical load using areverse phase control technique, the control circuit configured torender the controllably conductive device conductive at approximatelythe beginning of the half cycle of the AC power source and to render thecontrollably conductive device non-conductive at the transition timeduring the half cycle.
 9. The load control device of claim 8, wherein,when the control circuit is controlling the controllably conductivedevice using the reverse phase control technique, the control circuit isconfigured to control the communication circuit to provide the activepull-down state on the electrical wire during the period of time aroundthe transition time of the controllably conductive device.
 10. The loadcontrol device of claim 1, wherein the control circuit is configured tocontrol the controllably conductive device to control the amount ofpower delivered to the electrical load using a forward phase controltechnique, the control circuit configured to render the controllablyconductive device conductive at approximately the transition time duringthe half cycle.
 11. The load control device of claim 10, wherein, whenthe control circuit is controlling the controllably conductive deviceusing the forward phase control technique, the control circuit isconfigured to control the communication circuit to provide the activepull-up state on the electrical wire during the period of time aroundthe transition time of the controllably conductive device.
 12. The loadcontrol device of claim 1, wherein the period of time begins atapproximately the transition time of the controllably conductive device.13. The load control device of claim 1, wherein the period of timebegins before the transition time of the controllably conductive device.14. The load control device of claim 1, wherein a length of the periodof time is approximately 200 microseconds.
 15. The load control deviceof claim 1, wherein the control circuit is configured to determine thatthe remote control device is placing the electrical wire in the activepull-down state or the active pull-up state during the period of timearound the transition time to transmit a digital message.
 16. The loadcontrol device of claim 15, wherein the control circuit is configured tocontrol the communication circuit to provide the active pull-down stateon the electrical wire during the period of time around the transitiontime when the communication circuit is not transmitting a digitalmessage, and configured to determine that the remote control device isplacing the electrical wire in the active pull-up state during theperiod of time around the transition time to transmit a digital messagebecause the active pull-up state is stronger than the active pull-downstate.
 17. The load control device of claim 15, wherein the controlcircuit is configured to control the communication circuit to providethe active pull-up state on the electrical wire during the period oftime around the transition time when the communication circuit is nottransmitting a digital message, and configured to determine that theremote control device is placing the electrical wire in the activepull-down state during the period of time around the transition time totransmit a digital message because the active pull-up state is weakerthan the active pull-down state.
 18. The load control device of claim 1,wherein the period of time around the transition time of thecontrollably conductive device comprises a blanking time period.
 19. Aload control device for use in a load control system for controlling anamount of power delivered from an AC power source to an electrical load,the load control system comprising a remote control device adapted to becoupled to the load control device via an electrical wire, the loadcontrol device comprising: a controllably conductive device adapted tobe electrically coupled in series between the AC power source and theelectrical load; a control circuit configured to control thecontrollably conductive device to control the amount of power deliveredto the electrical load using a reverse phase control technique, thecontrol circuit configured to render the controllably conductive deviceconductive at approximately the beginning of a present half cycle of theAC power source and to render the controllably conductive devicenon-conductive at a turn-off time during the present half cycle; and acommunication circuit adapted to be coupled to the electrical wire, thecommunication circuit configured to conduct a charging current for apower supply of the remote control device through the electrical wire,the communication circuit responsive to the control circuit to controlthe electrical wire between an active pull-up state and an activepull-down state to transmit a digital message to the remote controldevice via the electrical wire; wherein the control circuit isconfigured to control the communication circuit to generate a highimpedance state on the electrical wire when the communication circuit isnot transmitting a digital message to the remote control device, thecontrol circuit further configured to control the communication circuitto provide the active pull-down state on the electrical wire during aperiod of time around the turn-off time of the controllably conductivedevice when the communication circuit is not transmitting a digitalmessage to the remote control device.
 20. The load control device ofclaim 19, wherein the control circuit is configured to determine thatthe remote control device is placing the electrical wire in the activepull-up state during the period of time around the turn-off time totransmit a digital message to the load control device because the activepull-up state is stronger than the active pull-down state.
 21. The loadcontrol device of claim 19, wherein the communication circuit comprisesa first switching circuit adapted to be coupled between the AC powersource and the electrical wire, the first switching circuit configuredto conduct the charging current for the power supply of the remotecontrol device through the electrical wire during a charging time periodof the present half cycle of the AC power source.
 22. A method forcontrolling an amount of power delivered from an AC power source to anelectrical load, for powering a power supply of a remote control devicewith a main load control device, and for communicating between the mainload control device and the remote control device, the main load controldevice comprising a controllably conductive device adapted to beelectrically coupled in series between the AC power source and theelectrical load, and the remote control device adapted to be coupled tothe main load control device via an electrical wire, the methodcomprising: rendering the controllably conductive device conductive atapproximately the beginning of a present half cycle of the AC powersource to conduct a charging current to charge the power supply of theremote control device through the electrical wire; rendering thecontrollably conductive device non-conductive at a turn-off time duringthe present half cycle to control the amount of power delivered to theelectrical load; and controlling the electrical wire between an activepull-up state and an active pull-down state to transmit a digitalmessage to the remote control device via the electrical wire; whereincontrolling the electrical wire comprises generating a high impedancestate on the electrical wire when the main load control device is nottransmitting a digital message to the remote control device, andcontrolling the electrical wire to be in the active pull-down stateduring a period of time around the turn-off time of the controllablyconductive device when the main load control device is not transmittinga digital message to the remote control device.